This invention relates to latex polymers and compositions incorporating such latices adapted for staining and/or sealing porous substrates such as wood.
Reduction of the amounts of organic solvents in coating compositions has been a desirable objective for the sake of reducing the amount of volatile organics released into the atmosphere. Therefore, waterborne coating compositions have come into widespread use. Waterborne stains have also been proposed (e.g., U.S. Pat. Nos. 4,432,797 and 4,976,782), but providing acceptable performance with a waterborne stain has generally been hampered by the tendency of water to raise the grain of the wood to which a waterborne stain is applied. Another problem is that in some cases the water soluble dyes that are used in waterborne stains can be redissolved by subsequently applied waterborne coatings.
In order to provide a barrier to hold out subsequently applied coatings, it is desirable for the stain to include a resin that at least partially seals the wood surface. Resins proposed for this purpose include aqueous polyvinyl chloride latex (e.g., "GEON" from B. F. Goodrich Co.), but they are not as satisfactory as would be desired because they require relatively high levels of organic solvent to aid coalescence of the latex particles to form a film, thereby limiting the reduction in volatile organic content. A further disadvantage is that the water-miscible organic solvents that are included for the sake of coalescence tend to increase penetration of the water into the wood, thereby worsening grain raising. Additionally, the prior art vinyl latex tends to be milky in appearance initially after spraying onto a substrate, which is undesirable because the applicator cannot observe the effect of the composition on the substrate so as to correct any deficiencies. The inclusion of ammonia or amines in prior art waterborne compositions is also believed to worsen the grain raising problem.
Additional features that are desirable in a stain composition include application properties such as low drag and workability, i.e., the ability to wipe the stain for a period of time before drying. One prior art approach to reduce grain raise is to increase the amount of pigment in the stain composition, but this tends to speed the drying rate, thereby undesirably decreasing the working time. It is known that the drying rate can be retarded by adding an oil to the composition, but the oil can have a negative effect on adhesion.